Magnetic Resonance Imaging Sequences

An MRI sequence is a number of radiofrequency pulses and gradients that result in a set of images with a particular appearance. This article presents a simplified approach to recognizing common MRI sequences, but does not concern itself with the particulars of each sequence.
abdominal mri sequences
abdominal mri sequences radiology
acronym mri sequences
adni mri sequences
advanced mri sequences
all mri sequences
ankle mri sequences
aortic dissection mri sequences
avascular necrosis mri sequences
MRI Sequences
MRI Signal production
MRI Interpretation
MRI Pulse Sequences
T1, T2, PD weighted Imaging
Spin Echo
Fast and Ultrafast MRI
Fast (Turbo) Spin echo
Inversion recovery sequence
STIR Sequences
FLAIR Sequence
Greadient sequence
3d greadient echo
Echo planar imaging sequence
Dynamic imaging
basic mri sequences radiographics
blade sequence mri
blood mri sequences
blood sensitive mri sequences
Functional Imaging (fMRI)
Diffusion weighted imaging (DWI)
MR Spectroscopy
Magnitization transfer (MT) MRI
MRA & MRV
MR Perfusion
Susceptibility weighted imaging
T1 rho imaging
Fat Suppression imaging
SPAIR
SPIR
Signal to noice ratio
Radiofrequency (RF) coils
Water excitation and Dixon Method
MRI Abbreviation
Overview
The simplest way to think about the multitude of sequences available on modern scanners is to divide them according to the dominant influence on the appearance of tissues. This leads to a division of all sequences into proton density (PD) weighted, T1 weighted, T2 weighted, diffusion weighted, flow sensitive and 'miscellaneous'. A number of 'optional add-ons' can also be considered, such as fat or fluid attenuation, or contrast enhancement. This leads to a broad categorisation as follows:
T1
gadolinium enhanced
fat suppressed
T2
fat suppressed
fluid attenuated
susceptibility sensitive
proton density
fat suppressed
diffusion weighted
flow sensitive
MR angiography
MR venography
CSF flow studies
miscellaneous
MR cholangiopancreatography (MRCP)
a special T2-weighted sequence
MR spectroscopy
MR perfusion
functional MRI
tractography
Terminology
Intensity
When describing most MRI sequences we refer to the shade of grey of tissues or fluid with the word intensity, leading to the following absolute terms:
high signal intensity = white
intermediate signal intensity = grey
low signal intensity = black
Often we refer to the appearance by relative terms:
hyperintense = brighter than the thing we are comparing it to
isointense = same brightness as the thing we are comparing it to
hypointense = darker than the thing we are comparing it to
Annoyingly these relative terms are used without reference to the tissue being used as the comparison. In some instances this does not lead to any problems; for example, a hyperintense lesion in the middle of the liver is clearly hyperintense compared to the surrounding liver parenchyma. In many other situations however use of relative terms leads to potential confusion. Imagine a lesion within the ventricles of the brain described as "hypointense". Does this denote a lesion darker than CSF or than the adjacent brain?
As such it is preferable to either use absolute terminology or, if using relative terms, to acknowledge the comparison tissue e.g. "the lesion is hyperintense to the adjacent spleen".
NB: the word density is for CT, and there are few better ways to show yourself as an MRI noob than by making this mistake.